Fluid can be obtained from different sources, one of which is a pump that receives a fluid from a fluid supply, displaces the fluid with a mechanical means, and provides the fluid to, for example, a conduit. The mechanical means employed by the pump may be a member with a reciprocal motion, such as pistons, peristaltic rotors, or the like. The reciprocal motion periodically displaces the fluid towards the conduit, thereby causing the fluid to flow. Due to the reciprocal motion, the fluid provided by the pump may have pulses that are carried downstream through the conduit. Accordingly, the pulses are sometimes referred to as fluid born noise (“FBN”). There are other noise sources of FBN such as, for example, nearby vibrating machinery, vibrations from the environment due to being in the moving vehicle, such as a rail car, or the like. Fluid flow with the FBN is commonly referred to as a pulsating flow.
The pumps are typically used in fluid control systems with a valve. The valve may be a proportional valve, although many other valves or flow controllers may be employed with the pumps. For example, a proportional valve downstream from the pump may control a flow rate of the fluid with a flow sensor. More specifically, the flow sensor may measure the flow rate of the fluid flowing through the conduit and provide a flow rate signal to the valve. The flow rate signal can be proportional to the measured flow rate of the fluid. Using the flow rate signal, the proportional valve may control the flow rate of the fluid through the conduit.
However, due to the FBN, the flow rate signal may also include noise. The noise can cause the flow controller to be unstable. For example, a position of the proportional valve may not correspond to a flow rate set point and, instead, may continuously oscillate about the set point. Accordingly, it is desirable to attenuate the pulses in the pulsating flow so the flow rate may be stable.
Some fluid control systems employ a signal from, for example, a pressure transducer to attenuate the pulses. More specifically, the pressure transducer may measure the pulses in the pulsating flow and provide a noise signal that corresponds to the pulses in the pulsating flow. The noise signal may be used to provide a noise reference employed to generate a signal that, when applied to the pulsating flow, cancels the pulses. In effect, the signal applied to the pulsating flow is a cancelling signal. The cancelling signal may be 180 degrees out of phase with the noise reference and, therefore, 180 degrees out of phase with the pulses. Accordingly, the fluid flow becomes more smooth, thereby providing a more stable fluid flow.
However, the pressure transducer may not have sufficient bandwidth to convert all of the pulses into the noise reference. For example, the pulses may have high frequency components that are greater than the cutoff frequency of the pressure transducer's passband. In addition, the pressure transducer is a separate device from the pump and other components in the fluid control system. As a result, the pressure transducer is an additional undesirable hardware cost.
Since the noise source (e.g., pump, vibrating machinery, moving vehicle, etc.) is the source of the pulses in the pulsating flow, the noise source could provide the noise reference. In other words, the noise reference may be a source noise reference. As a result, the noise reference provided by the noise source may include all of the frequencies associated with the pulses in the pulsating flow. Other benefits may also be realized if the source could be employed as a noise reference. Accordingly, there is a need for active cancellation of pulsating flow with a source noise reference.